Well if you really mean literarly what you ask then no. No mel can not be pre compiled, it can just be translated. Howeevr theres really no reason to do this, cant fo earth of me find any use for it its not like youd gain anything form it really.
This said i think you dindt mean exactly what you typed. You meant that you wanted to just have the script loaded. Sure you can do that, just load it in userSetup.mel However theres very little need to do that unless yoru launching some gui components. Maya knows to load the script once needed, provided that you put the mel file in the right place and name it according to your launc function. And yes you can also source things form a plugin, but thats just stupid, it gives you just more overhead,*
- and no under no circumstances can you hide what your doing. If you wrote it down then anybody you give the script/plugin to can read exactly what you did. This is a property of all code, just mroe so with maya api. Same applies to python, even if you jsut distribute teh pyc I canb still convert it back to human readable python code. And in c i can just firte it up in a debugger.